The present invention relates to a configuration for a semiconductor device intended for a power transistor module used with an inverter.
These days, power transistor modules with diverse specifications and configurations used in the field of power electronics are produced commercially. FIGS. 6 and 7 show examples of conventional power transistor modules, FIG. 6 showing a one-set module, and FIG. 7 showing a two-set module,--the appearance of the modules is shown in FIGS. 6(a) and 7(a) and the internal circuitry is shown in FIGS. 6(b) and 7(b). Actual products use the transistors in Darlington connection and contain high-speed diodes for free wheeling between a collector and an emitter. FIGS. 6 and 7 show a resin made case 1, a metallic base plate 2, main terminals 3 for a collector terminal C and an emitter terminal E, auxiliary terminals 4 for drive signal input, and case fixing screw holes 5 disposed at the four corners of the case 5, wherein the main terminals 3 and the auxiliary terminals 4 are disposed on the top face of the case 1, and the auxiliary terminals 4 are arranged on a parallel level of the upper face one step lower than the main terminals 3.
In the structure shown in FIG. 6, a partition 1a is disposed between the main terminals 3 to ensure a sufficient insulation creepage distance. In contrast, the structure in FIG. 7 has grooves formed among the main terminals 3. When assembling circuits such as for an inverter combining two or more transistor modules with the above structures, the transistor modules are either interconnected in series or parallel by connecting the main terminals with busbars.
Recent trends in manufacturing products such as inverters are popularizing a method of assembling products using automatic mounting in assembly lines. Printed wiring boards are being used in place of conventional busbars to interconnect transistor modules in order to simplify the assembly process. To explain, mounting transistor modules on a printed wiring board on which the necessary conductor patterns for the main circuit have already been formed can greatly reduce the number of parts and the worker man-hours compared with a busbar wiring system. For example, a snubber circuit and a control circuit can be mounted on the printed wiring board at the same time using a printed wiring board enabling products to be made more compact.
However, the following problems need to be solved for transistor modules of conventional structure, shown in FIGS. 6 and 7, when a printed wiring board is used for wiring the modules. That is, in the conventional structures of FIGS. 6 and 7, the height of the main terminals 3 and the auxiliary terminals 4 are different, and in the structure of FIG. 6 the partition 1a protrudes from between the main terminals 3, whereby the printed wiring board 8 cannot be mounted close to the casings of the transistor modules because the partition 1a works as an obstacle, and the printed wiring board cannot be connected directly to the terminals by means of screwing.
Another problem is that while the case fixing screw holes 5 are disposed at the four corners of the case 1 in the conventional structures, if the holes must be reduced to two, the auxiliary terminals 4 standing in a lateral line on the edge of the case 1 as in FIG. 7(a) form an obstacle and make disposing screw holes with the same diameter as the conventional holes on the center of both edges of the case 1 difficult in terms of dimensional restriction. The present invention has been made in light of these problems, and its objective is to solve said problems and provide a semiconductor module with good assembling workability suitable for mounting on a printed wiring board employed for interconnecting the modules when assembling inverter circuits using two or more transistor modules.